Orthodontic treatment of improperly positioned teeth involves the application of mechanical forces to urge the teeth into correct alignment and orientation. Such treatment typically involves use of orthodontic brackets which are small slotted bodies configured for direct attachment to the front or labial surfaces of the teeth, or alternatively for attachment to bands which are in turn cemented or otherwise secured around the teeth.
A resilient curved arch wire is then seated in the bracket slots, and the arch wire is bent or twisted before installation. The restoring force exerted by the seated resilient wire tends to shift the teeth into orthodontically correct alignment. Depending on the shape of the arch wire (both round and rectangular cross sections are in common use) and the orientation of the bracket slot, it is possible to apply forces which will shift, rotate or tip the teeth in any desired direction.
It is necessary to secure the arch wire in the bracket slot to insure that the wire is not displaced or dislodged when chewing food or brushing the teeth, or by application of other forces by the patient. Brackets are accordingly provided with tie wings which are cleatlike surfaces on opposite sides of the bracket slot, and around which a ligature wire or an elastic band can be anchored by the orthodontist to capture the arch wire in the bracket slot.
Conventional brackets thus have a gingival (gum facing) tie wing, and an occlusal (extending toward the tooth biting edge) tie wing, and known twin brackets have two pairs of such tie wings. More recently introduced brackets are of a triwing configuration with two spaced-apart tie wings on the occlusal side, and a single central tie wing on the gingival side which acts as a fulcrum.
An advantage of this triwing arrangement is that it enables the orthodontist to ligate the arch wire in a fashion which permits rotation of the associated tooth. Another advantage is that the bracket can be tapered (decreased in width gingivally) to match the natural tapered contour of the tooth. Another reason for the conventional triwing arrangement is that the single gingival tie wing, which is usually of relatively small cross section, is positioned away from occlusal forces which might break the wing away from the bracket body.
A disadvantage of conventional triwing brackets is that the two spaced-apart occlusal tie wings are of reduced cross section, and may not have sufficient strength to resist fracture due to occlusal forces. In most cases, breakage of a tie wing will require time-consuming replacement of the entire bracket to insure that the arch wire remains properly seated in the bracket slot. This problem is particularly noticeable in recently introduced brackets made of ceramic material which is brittle and susceptible to fracture upon application of heavy loads to bracket portions of thin cross section.
The bracket of this invention provides improved structural reliability and integrity by departing completely from the conventional triwing design which places the spaced-apart wings on the occlusal side. The improved bracket positions a strong and relatively wide single wing on the occlusal side of the bracket body, and places the spaced-apart wings (needed for rotation control) on the gingival side which is sheltered from heavy occlusal forces.